1. Field of the Invention
This invention relates to drilling derricks of the type used to drill oil and gas wells and especially relates to an improved crown block.
In drilling wells into the earth such as those in search of oil, gas or various minerals, it is common practice to provide a drilling derrick. This drilling derrick may be anywhere from twenty to one hundred or more feet in height. It will have what is called a crown block at the top. This crown block will have one or more sheaves over which a cable will be threaded. The cable will extend down to what is called a traveling block which is suspended by the cable underneath the crown block. One end of the cable is connected to the draw works which has a power drum for reeling and unreeling the cable and the other end of the cable is called a deadline and is connected to the deadline anchor.
The load which the traveling block must lift varies from a small amount when lightweight drill pipe in short sections are being lifted to when long sections of heavy duty large diameter casings are being lowered or raised into the well bore. As the crown block at the top of the derrick the entire derrick has to be made strong enough to support the heaviest loads. There are numerous disclosures in the patents and literature which discloses many different types of derricks and their construction, operations and so forth.
2. Description of the Prior Art
Typical of this art are the following patents: U.S. Pat. No. 1,487,608, Rowland, entitled "Crown Block for Well Drilling Apparatus" which has a shaft 4 fixed to the beams 1 for supporting several sheaves of the operating lines. U.S. Pat. No. 1,563,739, Goeser, entitled "Crown Block" has sheaves each mounted on its respective shaft 60 in which the shafts 60 are fixed to the structure. U.S. Pat. No. 2,187,392, Chapel, entitled "Derrick" which shows a pair of crown block units mounted movably on its upper end whereby one of the units may be centered within the derrick to support the drill pipe or tubing while the other unit may be off center free for other work. Each unit is complete in itself including the usual traveling block. U.S. Pat. No. 2,226,947, Sheldon, "Well Drilling Apparatus" which has crown blocks 33 and 34 which are independent of each other and each performs an individual and separate operation. U.S. Pat. No. 3,658,298, Moore et al, entitled "Drilling Rig With Shiftable Crown Blocks", and has two sets of hoisting mechanisms with two crown blocks which are shiftable to enable either block to be positioned over the drill hole. Each crown block has its independent traveling block, U.S. Pat. No. 4,074,774 Brown et al, entitled "Drilling Apparatus", is primarily concerned with an apparatus for drilling a slanting hole. U.S. Pat. No. 4,390,162, Woolslayer, entitled "Infinitely Variable Crown Block Positioning", which as the title indicates has as an object is to provide an oil well drilling derrick with a crown block that can be moved in a straight line into an infinite number of different positions for drilling wells wherever it is desired between opposite sides of the derrick. U.S. Pat. No. 4,423,994, Schefers et al, is entitled "Drilling Rig Equipped With Pairs of Block and Tackle Systems".